Part I : Level sensors retrofit.
The car is equipped with 2 levels sensors, both on the passenger side on my car. Check before purchasing because variant of the sensors exist for both sides, front and rear.
Parts needed:
REAR
1x 31288274 : level sensor, rear, right
3x 985919 : flange screw
FRONT
1x 31288272 : level sensor, front, right
2x 985919 : flange screw
1x 985590 : bolt
HARNESS
1x 31346736 : Connector housing
3x 31409244 : Repair terminal
1x 30767286 : Grommet, firewall
3x 30656698 : Repair terminal
As req. : 20AWG (0.35mm2) wire
As req. : Electrical harness tape
Heat shrink tubing, soldering supplies or wire splicing devices or your liking.
REAR : My car was already fitted with the correct wiring harness from factory for the rear sensor so this part is easy.
Remove wheel and look for a capped connector attached to the rear suspension arm.
Remove the protective cover and plug your level sensor. Then attach to the suspension using the flange screws. Mounting holes are already there so it’s only a matter of finding the correct orientation/geometry for the sensor lever and then screwing it down.
Make sure that all is nice and tight and reinstall wheel. Rear is done.
Pictures of the capped harness:
FRONT: After removing the wheel I was surprised to find out that there are various PNs for the control arm and that some don’t come with the mounting holes for the level sensor. Guess wich one I have 
So I had to improvise. First, finding a location that works with the sensor lever arm was not possible without modifying it. I had to heat the plastic lever just enough to twist it 90 degs axially. Then I had to make an hole in the control arm to attach the lever.
Not the best looking installation but it works and the sensor can work the complete movement range of the suspension. I was sure that I had a picture of this but no. I will take one when I change my winter wheels.
Now that the sensor is installed, an harness needs to be made to get the signals to the CEM, connector C1 (the green one). Since the CEM is located under the glove box, it’s relatively easy to get the harness to it coming to from the front right wheel.
Instead of attaching lots of picture, I will share this Volvo Accessories Instructions for adding fog lights to an XC60. Lots of steps are covered in there.
To get enough room to work around the CEM, the glove box needs to go out (steps 58+ in the PDF).
A rubber plug is present on the firewall, just under the foot of the passenger under the carpet and insulating foam (step 64 in the PDF). This plugs leads to an area between the engine compartment and the wheel well, conveniently close to the sensor (step 67). The rubber plug is to be replaced with a grommet that features nipples for wire routing (step 69).
To the harness, I soldered 6ft of wire to each of the 3 repair terminals (31409244) and inserted them at position 1,4 and 5 of the connector housing. This is the sensor side of the harness.
Label the free ends of the wires accordingly before going any further, this will spare you the trouble of finding which is which when connecting CEM side. Test fit the harness through the grommet and mark the length that needs to be taped, I removed the harness and applied harness tape to the complete length except the last few inches before the CEM connector.
I then reinstalled the harness through the grommet, clamping the nipple with a tie-wrap before over taping over the transition. I secured the harness with a few tie-wrap and connected it to the sensor. Put wheel back on.
You can do the connections on the CEM now or wait and do the headlight harness at the same time.
Sensor side (7/119)……………….CEM side (C1)
5—————————————–36
1—————————————–53
4—————————————–35
Cut your free end wire the proper length to get to the connector following the existing harnesses routing minus the repair terminal length. Solder then remove C1, unlock-it, insert the wire at the proper location, lock it back and reconnect (steps 69-72).
Front level sensor – done !